Influenza A viruses infect a variety of avian and mammalian hosts, including humans and pigs, and thus pose a significant pandemic threat. Vaccines against influenza viruses are available for both pigs and humans, with human vaccines receiving annual updates based on surveillance. These vaccines are designed to limit transmission and infection with host species-restricted variants within a single influenza A virus subtype, and they demonstrate efficacy within their respective populations. However, sporadic transmissions of influenza viruses across species barriers have been noted historically, with some of these events being associated with human pandemics. Since 2009, the emergence and pandemic classification of a triple reassortant influenza A virus (H1N1 subtype) containing swine, human, and avian genetic components raised greater concerns over future pandemics of swine-origin viruses. Specifically, there is a possibility that novel viruses could evolve within swine populations to yield viruses with increased transmissibility and virulence within humans. Since vaccination remains the primary means for controlling seasonal influenza viruses, combining our efforts to limit interspecies transmission events represents a likely path toward development of a pandemic vaccine. A vaccine that could limit the circulation of influenza viruses among pigs, as well as prevent interspecies transmission events from pigs to humans, would strengthen these efforts.
Seasonal influenza vaccines have historically demonstrated moderate effectiveness when the circulating strains closely match the vaccine strain, and the success of the vaccine can be compromised when there is not a close match. Efforts to generate vaccines that match circulating strains can be time-consuming, and in pigs the reformulation process of swine influenza vaccines is limited by the high cost of surveillance. Thus, a vaccine that can induce strong, broad, protective immunity toward heterologous strains is urgently needed in both pigs and humans.